[ryandrake]

Aren't game engines like Unity and Unreal only appropriate for first person shooters or third person adventure games? What about 2d platform games? Real time and turn based strategy games? Flight sims? Sports games? Board game remakes? You wouldn't choose a generic "game engine" for any of these, would you? Honest question, I'm not a game programmer, but as a programmer it sounds unlikely that a single package could be appropriate for so many different genres of games.

[wmil]

Hearthstone is done in Unity. Unity has a bunch of 2d platformer features these days.

What you're missing is that these big engines are also game development environments with extensive tools and integrated market places to purchase assets and features.

Learning Unity is learning an entire platform. It's a marketable skill.

Generally smaller developers don't have the development resources to roll custom everything. But modern platforms have enough spare hardware resources that the inefficiencies of Unity are worthwhile.

[hurricaneSlider]

There actually has been a lot of work done to make it suitable for use cases such as 2d, racing, etc.

An engine like unity basically provides utilities such as physically based rendering, camera systems, visual editors, scripting environments, a scenegraph editor, preview windows, io, asset import and conversion, audio, etc. Some games are of course easier to make than others in such engines, but they aren't that prescriptive.